Spectrometric analysis of solids



V- W 1953 J. A. HEPPLE, JR 2,659,823

SPECTROMETRIC ANALYSIS OF SOLIDS Filed Jan. 25, 1952 Y 2 Sheets-Sheet l I N VENTOR Johjiz'pple BY Zww/ZM AGE/V T Nov. 17,1953 J. A. HIPPLE, JR

SPECTROMETRIC ANALYSIS, OF SOLIDS 2 Sheets-Sheet 2 Filed Jan. 25, 1952 INVENTOR John Afizpple AGENT Patented Nov. 17,,1953

UNITED STATES OFFICE SPEGTROMETRIC ANALYSIS OF SOLIDS John A. Hipple, Jr.,. Chevy Chase, Md.,. assignor to'the United States of Americayas represented by the Secretary of Commerce Application January 25, I952, Serial.No-..2.68',323- 13 Claims. (01. 250-4119) (Granted under Title 35 11.8. Code (195%),

sec. 266) 1 The invention described herein may be manufactured and used by or for the Government of the United States for governmental purposes Without the payment to me of any royalty thereon inaccordance with the provisions of the act of March 3, 1883, as amended (45 Stat. 467; 35 U. S; 0.45).

The present invention relates to a mass spectrometer and more particularly to a mass spectrometer for the quantitative analysis of solids.

but the great variation in the intensity of the ion beam thus produced has restricted the spark source to methods employing photographic detection. The great variations in the intensity of the ion beam produced by the spark source have made it impossible to date to measure the quantity of one mass and then of another since there was no means for correlating the total number of ions present over the two periods of time. In the photographic methods, all of the masses to be measured are allowed to strike the photographic plate over the same period of time, each mass striking the plate at a different place because of separation in the magnetic field. Such methods are inherently limited in accuracy, convenience, speed, linearity of response, and range of concentrations that may be covered in one exposure. Moreover, the sensitivity of the photographic plate decreases for the heavier masses. These limitations have greatly restricted the use of mass spectrometers for theanalysis of solids and have deterred the introduction of this technique into analytical laboratories.

An object of the present invention is to provide a mass spectrometer for 1 the analysis of solids which automatically compensates for the variation in the intensity of the ion beam. Another object of the invention is to provide iiast and accurate means for the spectroscopic analysis of solids.

. 2 ventional mass spectrograph of the doublefocusing type is modified in several respects. A monitoring collector is placed at the entrance to the magnetic analyzer and it provides a measure of the total ion current entering the analyzer. The magnetic analyzer has a Single exit slit and i'o'nco'llector, and the various masses to be measured are swept'across this exit slit. The currents obtained from the two collectors are grounded through resistors and the voltages across these resistors are compared. An electrical rebalancing system responds to any changes in the relationship between these two voltages and re-- cords the ratios of the currents at the two 001 l'ectors. Since any change in ion current dueto fluctuations in the spark source will produce proportionalchangesin both currents, the ratio of the two currents will be relatively unaffected and the rebalancing system will not be energized.

Other uses and advantages of the invention will become apparent upon reference to the specifications and drawings.

Fi ure 1 is a side elevational view of the mass spectrometer.

Figure 2 is a top view of the machine taken along plane-'22 of Figure 1. s

Figure 3 is a view in perspective of the monitor collector.

Figure 4 is a top view of the monitor collector.

Figure 5 shows a diagrammatic cross section of the mass spectrometer and the machine's associated electrical apparatus.

Referring to Figures 1 and 2, l is the base of the machine. The two coils and magnetic poles that provide the magnetic field across the mag- Inetic analyzer 5 are housed in the casings 2 and 3 and the base I and are energized by the variable source of current 10. The magnetic analyzer is supported between the casings 2 and 3 and therefore is subjected to the magnetic field set up between the two poles. The spark source is enclosed in the metal housing 4. This source is convention and therefore is not shown in detail. The leads 6 and 1 carry the radio-frequency voltage needed to energize the spark source. The ions formed by the spark source are accelerated by the accelerating anode 8' which is located in the cylinder 9. The accelerating anode 8 (see Figure 5) ismade up of two plates H and [2 which have slits l3 and [4 through which the ion beam 16 passes. The double plate is used so as to reduce the solid angle at which the beam emerges from, the anode. The voltage for the accelerating anode is supplied between ground machine from the spark source area.

static analyzer i5 which turns the beam through a 45-degree angle is located in the 45-degree :elbow The electrostatic analyzer is made up of two curved plates 58 and I9 which are su plied with a direct-current voltage over leads 2| and 22. The electrostatic an lyzer directs the ion beam down the cylinder 26 and into the magnetic analyzer 5. Located at the entrance to the ma netic analyzer is the monitor collector 21 which is composed of plates 28, 29, and 3|. A perspective view of these is shown in Figure 3. The to plate narrows the beam of ions that will enter the ma netic analyzer by having a slit 32 which is smaller than the cross-sectional area of the cylinder 25. The plate 29, which is located directly below plate 28, is a suppressor, the function of which is to reducesecondary emission from the collector nlate 3|. The volta e for the suppressor is su plied by the battery through the lead 35. The slit in the suppressor is the sar e size as that in plate 28. The collector plate 3! is the l st in the stack of three plates. The length of the slit 33 in t is plate is shorter than those in plates 28 and 29 and therefore interrupts a art of the ion beam that assed throu h the slit 32. The purpose for this will be explained later. The relative sizes of the slits in plates 28 and 3| are shown by the top view of the monitor (collector in Figure 4. The top plate is again 28. As can be seen. p rt of 3| extends into-the openthe under the slit 32. The location of the monitor collector 27 with regard to the rest of the machine is shown in Figure 2. V The ion current collected on the late 3| is supplied to an amplifier over lead 34.

A final ion collector 35, Figure 5, is located in the cylinder 31 just behind the plate 35, and the ion current collected there is fed to an amplifier over lead 38.

The entire path through which the ion beam travels must be e acuated and therefore the outlet 39 is provided for connection to vacuum pumps. Since it is desirable to be able to replace the rod that is to be ionized by the spark source without losing the vacuum in the entire machine, means are provided for sealing off the rest of the A thumb screw 4! is connected to a slide valve 42 (Figure {5) which will cover the slit 23 when the thumb screw is turned. This seals 01? the spark area from the rest of the system. After the rod is replaced, this region can be evacuated through outlet 42. The thumb screw 43 controls the valve 44 in this outlet.

The operation of the mass spectrometer according to the present invention will be explained with reference to the diagrammatic cross section shown in Figure 5.

The material to be analyzed is formed into a rod 45 and ionized by a spark discharged between the rod, which forms one of the electrodes of the spark system, and the disk 41 which forms the other electrode. The radio-frequency oscillator 48 supplies the high voltage necessary for the creation of the spark discharge. The ions formed by the spark are accelerated. through the slits l3 and, M. The accelerating potential is supplied between the anode plates H and I2 and the electrode 41 by the voltage supply 49. The stream of ions emerging from the slit I4 enters the electrostatic analyzer l5 and is deflected through a 45-degree angle by the electrostatic field established between the deflection plates [8 and l The voltage for these plates is supplied by the voltage source 5|. The electrostatic analyzer acts upon the ion beam in such a way that only ions lying Within a definite predetermined energy range appear across the slit 32 in the plate 28. The ions with the lowest energy appear at the right side of the slit and those with the highest energy appear at the left side of the slit. The ions, after passing through the monitor collector, the operation of which will be explained later, enter the magnetic analyzer 5. The action of the magnetic field upon the ions is such that all ions of the same mass will appear at the same point along the diameter dd of the magnetic analyzer. By correctly choosing the intensity of the magnetic field the ions of the desired mass will pass through the slit in plate 35 and be collected by the final ion collector 36. So much or the operation as has already been described is old and well known in the art and is common to most double-focusing mass spectrometers.

The present invention is concerned with the operation of the monitor collector and its related parts. As previously stated, the vacuum spark, although an excellent source of ions from solid materials, gives a widly fluctuating ion beam current, and mass spectrometers using such a source have not been considered practical. To make it practical to use the spark source with a mass spectrometer the present invention uses a monitor collector placed at the entrance to the masnetic analyzer. The monitor collector provides a method of measuring the ions of all masses that enter the analyzer. Referring now to Fig ures 3 and 4, the ion beam, after passing through the entrance slit 32, passes through the slit 33 in the plate 3!. As previously stated, the entrance slit 32 determines the energy range of the ions that pass into the magnetic analyzer. This is controlled by the dimension (1 of the slit. On the other hand, the dimension 1) of the slit determines the magnitude of the ion current in that energy range that will pass into the magnetic analyzer. Since the a dimension of the slit 33 is at least as large as that of slit 32, while the b dimension is smaller, the plate 3| collects an ion current that has the same energy range as that passing into the magnetic analyzer. The portion of the ion current so collected contains ions of all the masses present and is directly proamplified by the direct-current, phase-inverter amplifier 52 and then applied across the resistor 53, which is a part of a standard Brown recorder 56. The ions of the particular mass that is of interest at the moment are collected at the collector 35 and the resulting current is applied across the resistor 54.

As previously stated the amplifier 52 is a phaseinverted amplifier and as a result the voltage applied to the resistor 53 is negative with respect to ground. However, the voltage applied across resistor 54 for the output of the final collector 35 is positive and therefore the voltages across the resistors 53 and 54 are in opposition. If the voltage across 54 is equal to the voltage across the portion of 53 between the slider 52 and ground, the point 51 will be at ground potential and there will be no input to the amplifier 58. When the magnitude of the ion current collected at col lector 35 changes, the voltage across the resistor 54 will change correspondingly. If an equal change in voltage has not taken place across that -;portion of resistor 53 .groundthere :isa si nal-input to thelamplifierl B.

.motor fil. .the -.voltages are again i'equal, :at which time the slider again indicates the ratiobetween-t-he two currents. .At-the same time the motor-drives-the slider it :drives the g-pen of the recorder thereby ,producing apermanent record. As diiferent magbetween rslider .62 land 'This is fed to amplifier Elly-whereit-is converted to alternatingcurrent, amplified,and fed to the .The -motor drives the slider 162 until netic fields areapplied across themagnetic vanalyzer, this being accomplished by varying the source -I Oshown inFigure 2 :diiferent masses will .be directed to the collector 3t. Since-.each mass will probablynbe present in diiferent amounts the electrical system will "be-energized untittheisy-stem isagainrebalanced, at which time'the slider .willindicate the correct ratio. Since-the monitoring collector receives an ion current composed of all masses, and the final collector receives the current corresponding-to only one mass at a time,

the two collectors receive'currents that fluctuate .in the same manner; that is, in the mannerrin which the source is fluctuating. Theanalysis is therefore comparatively free of'errorsdue to fluctuation in'the spark source. 'In'other Words, any changes due to fluctuations in the source will produce anequal change in voltages across the resistor '54 and across resistor 53 'between the slider and ground. Consequently no si nal will be introduced into't'he amplifier 58. As a result ".the'motorriil will not be energized, and thegraph will not show'any change. Thissystem therefore .minimizes-errors that would result from the flucby the monitor will be identical inevery respect with that collected by collector 35 except that the monitor current will contain ions of all .masses in the ion beam While the collector current will contain ions of only one mass.

The present invention is not restricted to use with a spark source. It may be used profitably with any source, since .no source will be absolutely stable over long periods of time.

It will be apparent that the embodiments shown are only exemplary and that various modifications can be made in construction and arrangement within the scope of my invention as defined in the appended claims.

Iclaim:

1. A mass spectrometer which comprises a first means for producing ions of diiferent masses from a substance, a second means for forming said ions into a beam, magnetic means for resolving the ion beam into beams of selected masses, a third means for producing a current that fluctuates in intensity in the same manner as the ion current in said magnetic means, a final collector, a fourth means including said magnetic means for directing one of said selected masses at a time to said final collector, and a fifth means for comparing the currents obtained from said third means and said final collector.

2. A mass spectrometer which comprises a first means for producing ions of difierent masses cfrom -a subtsanceyasecond means for iorming said ions into a beam, magnetic mean for -resolving the ion beam :into 'beams of selected masses, a third means for producinga current that fluctuates :in intensity in the same manner :as the total ion current in said magnetic means, ..c0llector means .for producing a current that fluctuates in thesame manner as .a beam of-said selected masses, a fourth :means includingsaid .magnetic means for directingone of saidselect- :ed masses at a time .to-said fifth-named collector (means and a fifth meansfor comparing the currentsobtained from said third means with the current obtained from said-collector means.

3. A mass spectrometer which comprises a first .means for producing ions of diiferent masses from :a substance, a secondmeans for forming said ions into an ion beam, magnetic means for resolving the ion beam into beams of selected masses, monitoring means comprising a collector which collects anion current that includesall masses produced by said first means, a finalcollector, a third means including said magnetic means for directing one of said selected masses vat-a time .tosaid .final collector, and means for comparing the'currents'obtained from said moni-- toring means and said final collector.

#l. A mass spectrometer which comprises .means for producing ions of different masses from a substance, means for forming said ions linto a :beam, a magnetic analyzer for resolving the ion beam into beams of selected masses, a monitor collector comprising a collector which produces .a current that fluctuates in the same manner as the total ion current entering said magnetic analyzer, a final collector, means including said magnetic analyzer for directing one of said selected masses at a time to said :final collector, and rebalancing mean for obtaining the ratio of the currents obtained from said .monitor collector and said final collector. f 5. A mass spectrometer which comprises means for producing ions of different masses from a substance, means for forming said ions into a beam, a magnetic analyzer for resolving the .ion beam into beams of selected masses, a .monitor collector comprisinga collector which produces a current that fluctuates in the same manner as the ion current entering said magnetic analyzer, a final collector, means including said magnetic analyzer for directing one of said selected masses at a time to said final collector, resistor means for forming voltages from the ion currents collected at the monitor col lector and the final collector, and means for comparing those voltages. I

6. A mass spectrometer which comprises means for producing ions of different masses from a substance, means for forming said ions into a beam, a magnetic analyzer for resolving the ion beam into beams of selected masses, a monitor collector located between said secondnamed means and said magnetic analyzer, said monitor collector comprising a collector which produces a current that fluctuates in the same manner as the ion current entering said magnetic analyzer, a final collector, means including said magnetic analyzer for directing one of said selected masses at a time to said final collector, resistor means for forming voltages from the ion currents collected at the monitor collector and the final collector, and rebalancing means for comparing those voltages.

7. A mass spectrometer comprising means for producing ions of different masses from a substance, means for forming the ions into a beam, a magnetic analyzer for resolving the ions of each mass into separate ion beams, a monitor collector comprising a first and a second plate located between said second-named means and said magnetic analyzer, said first plate having a slit which allows a portion of said ion beam to pass through said first plate, said second plate having a slit which is smaller in one dimension than the slit in said first plate, said second plate therefore collecting a portion of the ions passing through said first slit, the portion collected being proportional to the total passing through said second slit, a final collector, means including said magnetic analyzer for directing the separate ion beams to the final collector at different times, resistor means for producing electric signals proportional to the ion currents collected at said second plate and said final collector, and rebalancing means for determining the ratio between said electric signals.

8. A mass spectrometer comprising means for producing ions of difierent masses from a substance, means for forming the ions into a beam with a continuous energy spectrum, a monitor collector comprising a first plate and a second plate, said first plate having a defining slit, one dimension of which determines the portion of the energy spectrum that will pass the first plate, the other dimension of which determines the ion current of the energy spectrum that will pass, said second plate having a defining slit which is smaller in the second-named dimension than said first slit, a magnetic analyzer which resolves the ion beam passing the slit in said second plate into beams of selected masses, a final collector, means including said magnetic analyzer for presenting the beams of selected masses at the final ion collector one at a time, resistor means for producing electric signals proportional to the ion currents collected on said second plate and said final collector and rebalancing means for determining the ratio between said electric signals.

9. The invention according to claim 8 in which the monitor collector has a third plate located between said first plate and said second plate, said third plate having a potential negative with respect to said second plate.

10. The invention according to claim 9 in which the means for producing the ions is a spark source.

11. A double-focusing mass spectrometer comprising a spark source for producing ions of different masses from a substance, an electrostatic analyzer for forming said ions into a beam with a continuous energy spectrum, a magnetic analyzer for resolving the ion beam entering said magnetic analyzer into beams of selected masses a monitor collector located between said electrostatic and magnetic analyzers of said double-focusing mass spectrometer, said monitor collector comprising a collector that collects an ion current that is proportional to the ion current entering said magnetic analyzer, a final collector, means including said magnetic analyzer for presenting the beams of selected masses at the final ion collector one at a time, resistor means for producing electric signals proportional to the ion currents collected on said second plate and said final collector, and rebalancing means for determining the ratio between said electric signals.

12. A double-focusing mass spectrometer comprising means for producing ions of different masses from a substance, an electrostatic analyzer for forming said ions into a beam with a continuous energy spectrum, a magnetic analyzer for resolving the ion beam entering said magnetic analyzer into beams of selected masses a monitor collector located between said electrostatic and magnetic analyzers of said double-focusing mass spectrometer, said monitor collector comprising a first plate and a second plate, said first plate having a defining slit, one dimension 01' which determines the portion of the energy spectrum that will pass the first plate and the other dimension of which determines the magnitude of the ion current in the predetermined energy spectrum that will pass the first plate, said second plate having a defining slit which is smaller in the second-named dimension than said first slit, a final collector, means including said magnetic analyzer for presenting the beams of selected masses at the final ion collector one at a time, resistor means for producing electric signals proportional to the ion currents collected on said second plate and said final collector, and rebalancing means for determining the ratio between said electric signals.

13. The invention according to claim 12, in which the monitor collector has a third plate located between said first plate and said second plate, said third plate having a potential negative with respect to said second plate.

JOHN A. HIPPLE, JR.

No references cited. 

